Young Molting Chicken

I have a young hen called Rita, she’s a Blacktail Hybrid and is about 8 months old.

In the last few days I’ve notice a smooth bald patch (which is gradually getting bigger) on her lower breast area. I’ve checked her over for any signs of bugs or mites and can’t see any. I haven’t seen any of the other hens pecking her and the bald patch of skin is the normal light peach colour, unlike my other hen who has a red bottom from constantly pecking at it, so I don’t think it’s that. I don’t think it’s stress related, she’s one of three in a big huge garden with plenty of food and space. Her comb is a healthy red, her poo looks normal and she’s just as hyper as ever, running all over the place like a lunatic and jumping up on everything. She’s also still laying an egg nearly every day.
I know most chickens naturally molt every now and again, but isn’t she too young? I’m really concerned at the moment because she’s very small for her age and it’s getting really cold outside. Do you think this bald patch is normal? Is there anything I can do to protect her from the cold?
Any advice or feedback would be much appreciated.

Molting normally starts at the head and neck, then moves lower. This sounds more like she is rubbing the feathers off somehow, or is plucking them in preparation for setting on eggs, or going broody. She certainly doesn't sound like her behavior is broody, though. Does she sleep on a roost? I think they can get something like this if they sleep on the ground.

I wouldn't worry a lot about the cold. Lots of chickens molt in late fall or winter.

She's never been keen on purching, most of the time she sleeps in the nesting box on the straw. So could it perhaps be an infection from sleeping on the straw? Do hens normally pluck their feathers to sit on eggs?

Hens will tuck feathers from their own bodies to use in their nest but usually they don't pluck so many that they go bald. I've never known hens to have an infection from straw, I use it all the time with my birds, unless there is pesticide or something in the straw making them itch.